Field of the Invention
The present invention relates to a printed wiring board, a printed circuit board, and an electronic device.
Description of the Related Art
Reduction in size and high functionality of electronic devices have led to reduction in size of a printed circuit board built in the electronic devices. In order to realize reduction in size of a printed circuit board, thinner wirings are employed in a printed wiring board of the printed circuit board, and the size of an electronic component such as a semiconductor device mounted thereon has been reduced. Further, a packaging density of electronic components has increased.
Therefore, in recent years, a ball grid array (hereafter, referred to as BGA) package, a land grid array (hereafter, referred to as LGA) package, or the like is used as a package of a high functionality semiconductor device.
The BGA package and the LGA package have the structure in which lands provided on a printed wiring board and lands provided on the undersurface of a package are joined by solder therebetween. When a semiconductor device operates, since a package is subjected to thermal deformation due to heat generation, a stress occurs at a junction between the package and the printed wiring board. Further, a stress due to deformation may occur not only at the junction but also at peripheral members such as a land provided on the undersurface of the package, solder, a land on the printed wiring board, and a wiring connected to a land. In order to suppress a break of members around a junction due to a stress caused by thermal deformation or the like occurring in such a way, various technologies have been proposed.
Japanese Patent Application Laid-open No. 2001-230513 discloses structure in which a gap is provided between an edge of a land of a printed wiring board and an edge of an opening of a solder resist film and thereby solder flows around into a side surface of the land when joining by soldering. This structure may improve the joining strength against warping and bending.
Japanese Patent Application Laid-open No. H10-214911 discloses structure in which the peel strength of a land is improved by covering both edges in the longer axis direction of the land with an insulating film.
In recent years, due to a demand for further reduction in size and high functionality of electronic devices, such structure may be employed that thinner wirings are drawn from lands of a printed wiring board.
Thus, improvement of the strength against a stress caused by thermal deformation may be demanded also for a wiring drawn from a land.